Heavy commercial vehicles and buses -- Steady-state rollover threshold -- Tilt-table test method

ISO 16333:2011 specifies a tilt-table test method for estimating the steady-state rollover threshold of a heavy commercial vehicle or bus, i.e. the maximum lateral acceleration that the test vehicle could sustain in steady-state turning without rolling over. ISO 16333:2011 is applicable to complete roll units/combinations of roll-coupled vehicle units, e.g. single-unit vehicles, tractor semitrailer combinations, articulated buses, full trailers, B-train combinations, of commercial vehicles, commercial vehicle combinations, buses or articulated buses as defined in ISO 3833, and under Categories M3, N2, N3, O3 and O4 of ECE and EC vehicle regulations (trucks and trailers with maximum weights above 3,5 t and buses and articulated buses with maximum weights above 5 t). ISO 16333:2011 does not cover transient, vibratory or dynamic rollover situations; nor does it consider the influences of dynamic stability control systems. Furthermore, the quality of the estimate of the steady-state rollover threshold provided by the test method decreases as the tilt angle required to produce rollover increases. Even so, the results for heavy vehicles with high rollover thresholds can be used for comparing their relative steady-state roll stability.

Véhicules utilitaires lourds et autobus -- Seuil statique de renversement -- Méthode d'essai du plateau incliné

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Status
Published
Publication Date
10-Feb-2011
Current Stage
6060 - International Standard published
Start Date
03-Feb-2011
Completion Date
11-Feb-2011
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INTERNATIONAL ISO
STANDARD 16333
Second edition
2011-02-15
Heavy commercial vehicles and buses —
Steady-state rollover threshold — Tilt-
table test method
Véhicules utilitaires lourds et autobus — Seuil statique de
renversement — Méthode d'essai du plateau incliné
Reference number
ISO 16333:2011(E)
ISO 2011
---------------------- Page: 1 ----------------------
ISO 16333:2011(E)
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ii © ISO 2011 – All rights reserved
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ISO 16333:2011(E)
Contents Page

Foreword ............................................................................................................................................................iv

Introduction.........................................................................................................................................................v

1 Scope......................................................................................................................................................1

2 Normative references............................................................................................................................1

3 Terms and definitions ...........................................................................................................................1

4 Principle .................................................................................................................................................2

5 Variables.................................................................................................................................................4

6 Measuring equipment ...........................................................................................................................4

6.1 General ...................................................................................................................................................4

6.2 Description.............................................................................................................................................4

6.3 Data processing.....................................................................................................................................5

7 Test conditions ......................................................................................................................................5

7.1 General ...................................................................................................................................................5

7.2 Tilt-table properties...............................................................................................................................5

7.3 Ambient conditions...............................................................................................................................5

7.4 Test vehicle ............................................................................................................................................5

8 Test procedure.......................................................................................................................................6

8.1 Installation of vehicle on tilt-table .......................................................................................................6

8.2 Test tilts..................................................................................................................................................7

9 Data analysis..........................................................................................................................................8

9.1 General ...................................................................................................................................................8

9.2 Tilt-table ratio.........................................................................................................................................8

9.3 Optional data presentations.................................................................................................................8

Annex A (normative) Test report — Additional test conditions...................................................................12

Annex B (informative) Error sources ..............................................................................................................13

© ISO 2011 – All rights reserved iii
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ISO 16333:2011(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies

(ISO member bodies). The work of preparing International Standards is normally carried out through ISO

technical committees. Each member body interested in a subject for which a technical committee has been

established has the right to be represented on that committee. International organizations, governmental and

non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the

International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.

The main task of technical committees is to prepare International Standards. Draft International Standards

adopted by the technical committees are circulated to the member bodies for voting. Publication as an

International Standard requires approval by at least 75 % of the member bodies casting a vote.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent

rights. ISO shall not be held responsible for identifying any or all such patent rights.

ISO 16333 was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee SC 9, Vehicle

dynamics and road-holding ability.

This second edition cancels and replaces the first edition (ISO 16333:2004), of which it constitutes a minor

revision.
iv © ISO 2011 – All rights reserved
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ISO 16333:2011(E)
Introduction

The main purpose of this International Standard is to provide repeatable and discriminatory test results.

The dynamic behaviour of a road vehicle is a very important aspect of active vehicle safety. Any given vehicle,

together with its driver and the prevailing environment, constitutes a closed-loop system that is unique. The

task of evaluating the dynamic behaviour is therefore very difficult since the significant interaction of these

driver-vehicle-environment elements are each complex in themselves. A complete and accurate description of

the behaviour of the road vehicle must necessarily involve information obtained from a number of different

tests.

Since this test method quantifies only one small part of the complete vehicle handling characteristics, the

results of these tests can only be considered significant for a correspondingly small part of the overall dynamic

behaviour.

Moreover, insufficient knowledge is available concerning the relationship between overall vehicle dynamic

properties and accident avoidance. A substantial amount of work is necessary to acquire sufficient and

reliable data on the correlation between accident avoidance and vehicle dynamic properties in general and the

results of these tests in particular. Consequently, any application of this test method for regulation purposes

will require proven correlation between test results and accident statistics.
© ISO 2011 – All rights reserved v
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INTERNATIONAL STANDARD ISO 16333:2011(E)
Heavy commercial vehicles and buses — Steady-state rollover
threshold — Tilt-table test method
1 Scope

This International Standard specifies a tilt-table test method for estimating the steady-state rollover threshold

of a heavy commercial vehicle or bus, i.e. the maximum lateral acceleration that the test vehicle could sustain

in steady-state turning without rolling over.

It is applicable to complete roll units/combinations of roll-coupled vehicle units — e.g. single-unit vehicles,

tractor-semitrailer combinations, articulated buses, full trailers, B-train combinations — of commercial vehicles,

commercial vehicle combinations, buses or articulated buses as defined in ISO 3833, and under Categories

M3, N2, N3, O3 and O4 of ECE and EC vehicle regulations (trucks and trailers with maximum weights above

3,5 t and buses and articulated buses with maximum weights above 5 t).

It does not cover transient, vibratory or dynamic rollover situations; nor does it consider the influences of

dynamic stability control systems. Furthermore, the quality of the estimate of the steady-state rollover

threshold provided by the test method decreases as the tilt angle required to produce rollover increases. Even

so, the results for heavy vehicles with high rollover thresholds can be used for comparing their relative steady-

state roll stability.
NOTE For further limitations of the specified test method, see Annex B.
2 Normative references

The following referenced documents are indispensable for the application of this document. For dated

references, only the edition cited applies. For undated references, the latest edition of the referenced

document (including any amendments) applies.
ISO 3833, Road vehicles — Types — Terms and definitions
ISO 8855, Road vehicles — Vehicle dynamics and road-holding ability — Vocabulary

ISO 15037-2:2002, Road vehicles — Vehicle dynamics test methods — Part 2: General conditions for heavy

vehicles and buses
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 8855 and ISO 15037-2, and the

following apply.
3.1
critical tilt angle
angle at which critical wheel lift occurs
3.2
critical wheel lift

first moment at which one or more wheels lift from the table surface, following which, stable roll equilibrium of

the vehicle cannot be established
© ISO 2011 – All rights reserved 1
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ISO 16333:2011(E)
3.3
roll unit

essentially self-supporting combination of roll-coupled vehicle units, the combination being free to roll

independently of other units

NOTE Typically, vehicle units joined by fifth-wheel couplings (which provide roll coupling) belong to the same roll unit,

while vehicle units joined by pintle hitches (which do not provide roll coupling) belong to different roll units. Roll units

including converter dollies could require minor vertical support at the drawbar pintle hitch.

3.4
steady-state rollover threshold

maximum magnitude of lateral acceleration that a vehicle can sustain during steady-state cornering on a flat

surface without rolling over
3.5
tilt angle

angle between the horizontal and a vector that is in the plane of the tilt-table surface and is perpendicular to

the tilt axis
3.6
tilt-table

apparatus for supporting a vehicle on its tyres on a nominally planar surface and for tilting the vehicle in roll by

tilting that surface about an axis nominally parallel to the X-axis of the vehicle

NOTE A tilt-table can be composed either of a single structure supporting all tyres of the vehicle on a contiguous

surface or of multiple structures supporting one or more axles on separate, but nominally coplanar, surfaces.

3.7
tilt-table ratio
TTR
tan (φ ), i.e. tan(φ ), at the occurrence of critical wheel lift
Tc T
3.8
trip rail

rail or kerb fixed to the tilt-table surface and oriented longitudinally beside the low-side tyre(s) in order to

prevent the tyre(s) from sliding sideways
3.9
wheel lift of the i axle

condition in which either all left or all right tyres of the i axle are out of contact with the surface of the tilt-table

NOTE It is a logical variable with values of 1 (true) or 0 (false).
4 Principle

The tilt-table test is a physical simulation of the roll-plane behaviour of a vehicle in a quasi-steady-state turn of

gradually increasing severity. In this test, the vehicle is mounted on a tilt-table with the vehicle's longitudinal

axis located parallel to an axis about which the table can be tilted. The tilt-table is then gradually tilted up to

the point at which the vehicle becomes unstable in roll. Safety restraints are used to prevent the actual rollover

of the vehicle.

When the table is at a non-zero tilt angle, the test simulates a non-vibratory steady turn. As shown in Figure 1,

the component of gravitational forces parallel to the table surface provides a simulation of the centrifugal

forces experienced by a vehicle in turning manoeuvres. The progressive application of these forces by slowly

tilting the table serves to simulate the effects of quasi-statically increasing lateral acceleration in steady turning

manoeuvres.
2 © ISO 2011 – All rights reserved
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ISO 16333:2011(E)

When the table is tilted, the centrifugal force is simulated by the component of the gravitational force parallel

to the table surface, m⋅g⋅sin(φ ), and the weight of the vehicle is simulated by the component of the

gravitational force that is perpendicular to the table, m⋅g⋅cos(φ ), where m is the mass of the vehicle, g is the

gravitational acceleration and φ is the tilt angle. Since the primary mechanism of actual rollover depends on

the ratio of the centrifugal forces to the vertical forces, it is appropriate to take the ratio of the simulated lateral

acceleration forces to the simulated weight to represent the lateral acceleration. At the moment of roll

instability, i.e. when critical wheel lift occurs, the tangent of the tilt angle, i.e. the tilt-table ratio (TTR), is an

estimate of the steady-state rollover threshold, expressed in gravitational units:

mg⋅⋅ sinφ
TTR≡=tanφ (1)
mg⋅⋅ cosφ

As the vehicle is progressively tilted during the tilt-table test, vertical load is progressively transferred from

tyres on one side of the vehicle to tyres on the other side. Tyres on the unloaded side will eventually lift off of

the table surface. Typically, wheel lift does not take place simultaneously for all axles; rather, lift-off occurs at

different axles at different angles of tilt. Tyres that lift off of the table early in the process may rise well off the

table surface before the critical wheel lift occurs and the vehicle becomes unstable in roll. It is often the case

that the vehicle will become unstable even though all tyres of one or more axles (often the steer axle) remain

firmly on the table surface. The tilting motion of the table should be stopped simultaneously with the vehicle

becoming unstable in roll, and safety restraints should be arranged to arrest the roll motion of the vehicle

immediately following that critical tyre-lift event.

Annex B presents further discussion of the tilt-table test method dealing with conceptual and practical sources

of error.
Key
1 simulated centrifugal force = m⋅g⋅sin(φ )
2 actual weight = m⋅g
3 simulated weight = m⋅g⋅cos(φ )
Figure 1 — Schematic diagram of tilt-table test
© ISO 2011 – All rights reserved 3
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ISO 16333:2011(E)
5 Variables
The following variables shall be determined:
a) wheel lift at each axle (l );
b) tilt angle at each axle of the vehicle (φ ).

Alternatively, where it is independently assured that all values of φ are within a range of ± 0,1°, tilt angle (φ )

Ti T
shall be determined.

Some or all of the following variables should be determined, in order to aid in analysing the vehicle’s

behaviour:

⎯ roll angle(s) relative to the tilt-table surface at relevant positions on the sprung mass(es);

⎯ roll angle(s) relative to the tilt-table surface of unsprung mass(es);
⎯ lateral suspension deflections;
⎯ tyre deflections;
⎯ air-spring pressures;
⎯ lateral deflections of relevant elements of the chassis or payload.

It is also recommended that the data record include event markers to indicate the occurrence of significant

events of interest, e.g. the transition through spring lash.
6 Measuring equipment
6.1 General
Measurement and recording equipment shall be in accordance with ISO 15037-2.
6.2 Description

All variables shall be measured by means of appropriate transducers, whose time histories should be

recorded by a multi-channel recording system. Typical operating ranges and recommended maximum errors

of the transducer recording systems for the variables not listed in ISO 15037-2 are shown in Table 1.

Table 1 — Typical operating ranges and recommended maximum errors of variables
not listed in ISO 15037-2
Recommended max. error
Variable Typical operating range
of combined system
Tilt angle(s) 40° ± 0,1°
Roll angles relative to the tilt-table surface 15° ± 0,1°
Lateral deflections ± 50 mm ± 1 mm
Air-spring inflation pressures 1 500 kPa 15 kPa
4 © ISO 2011 – All rights reserved
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ISO 16333:2011(E)
6.3 Data processing

The tilt-table test is a quasi-static test so that data processing concerns relating the natural frequencies of

vehicle responses and the frequency response of the instrument system do not apply in the usual manner.

However, the bandwidths of the analog data systems and the sampling rates of digitising systems, in

relationship to the maximum tilt rate of the table and the maximum roll rates of the vehicle and its components,

influence the overall accuracy of the measurement system. Specifications should be in accordance with

ISO 15037-2. In any case, the time response and latencies of all analog and digital elements of the

measurement system shall be properly considered in evaluating measurement accuracy.

7 Test conditions
7.1 General

Limits and specifications for the tilt-table, ambient conditions and vehicle test conditions indicated below shall

be maintained during the test. Any deviations shall be reported in the test report.

7.2 Tilt-table properties

The tilt-table facility shall have the properties given in Table 2. In addition, the tilt-table facility shall provide

lateral constraint of the vehicle through adequate surface friction or, optionally, through the use of a trip rail, as

specified in 8.1.2.
Table 2 — Tilt-table requirements
Property Requirement
Tilt angle variance at the positions of axle support ± 0,1°
Pivot axis alignment
Overall: Horizontal within ± 0,25°
Multiple axle tables: Co-linear within ± 2,5 mm
Minimum tilt rate < 0,05°/s

NOTE Specification of tilt angle variance implies requirements on table stiffness,

surface flatness and/or alignment of individual axle tables (see Annex B).
7.3 Ambient conditions
The ambient wind speed shall be u 2m/s.

Since, in certain cases, the temperature of vehicle components may influence test results, ambient

temperature shall be reported.
7.4 Test vehicle
7.4.1 General
The test vehicle shall be a complete, single roll unit.

The specifications of ISO 15037-2 shall apply except that items relating to test-induced changes in tyre

properties and to conditions and adjustments of the engine are moot. Items relating to other components of

the drive train may also not apply.
© ISO 2011 – All rights reserved 5
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ISO 16333:2011(E)
7.4.2 Self-regulating suspensions

For the standard test condition, if the test vehicle is equipped with height- or load-regulating suspensions,

suspension ride height or load shall be appropriately established before testing begins, and the active

adjustment function of the suspension shall be disabled during testing. Optionally, in some cases, e.g. when

the regulating system has a relatively fast response, it may be appropriate to allow self-regulation functions to

remain active during the tilt test. In either case, the state of the self-regulation shall be reported. Annex B

includes discussion on disabling self-regulating suspension features.

For height-regulating suspensions, reliable means shall be provided to identify the proper ride height within

± 5 mm during manual inflation. For load-regulating suspensions, reliable means shall be provided to identify

the proper inflation pressure within ± 5 % or ± 10 kPa, whichever is greater, during manual inflation.

8 Test procedure
8.1 Installation of vehicle on tilt-table
8.1.1 Alignment

For the standard test condition, the X-v-axis of each vehicle unit shall be parallel to the table pivot axis within

± 50 mm at each axle and, when applicable, at the coupling joints.
8.1.2 Lateral constraint

For the standard test condition, the surface of the tilt-table shall be such that tyre friction is adequate to

preclude the vehicle sliding sideways at the critical tilt angle. Additional safety restraints should be used to

arrest lateral motion in the event that the vehicle were to slide sideways on the table surface.

Optionally, a trip rail of any height up to the specified maximum may be provided immediately adjacent to the

low-side tyre of each axle such as to prevent the vehicle from sliding sideways at high tilt angles. The

maximum height of the trip rail shall be either 60 mm or two-thirds of the height between the wheel rim and the

tilt-table, whichever is larger. If a trip rail is used, the geometry of the trip rail shall be recorded.

NOTE 1 Table surfaces that achieve friction coefficients approaching unity are available. See Annex B.

NOTE 2 The use of trip rails can be expected to influence the result of the test by increasing TTR slightly. See Annex B.

8.1.3 Longitudinal constraint

Longitudinal constraint of the vehicle shall be accomplished by constraints applied at one, and only one, axle.

When applicable, the transmission shall be in neutral and differential locks shall not be applied.

The proper response of heavy vehicle suspensions during tilt tests typically requires small, but free

longitudinal motion of the axles. When individual axle tables are used, care should be taken that such motion

can safely take place on the surfaces of the tables.

If longitudinal constraint is provided by blocking tyres of a steering axle, the steering system should be locked

appropriately. In any case, it is also recommended that additional safety constraints be used, such as slack,

longitudinal cables or chains applied to one or more axles near the low-side tyres.

8.1.4 Roll restraints

Safety restraints shall be provided that are capable of fully arresting the roll motion of the test vehicle

immediately after critical wheel lift occurs.
6 © ISO 2011 – All rights reserved
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ISO 16333:2011(E)
8.1.5 Auxiliary vertical support

Some test vehicles require auxiliary vertical support at the coupling joint. For example, a semitrailer coupled to

a converter dolly requires support of the dolly drawbar at the pintle hitch. In such cases, a mechanism shall be

provided that

a) provides the necessary vertical support in a manner representative of normal use,

b) maintains lateral position according to 8.1.1, and
c) provides no significant roll coupling at the support point.
8.1.6 Suspension condition
8.1.6.1 Neutral roll condition

It is recommended that, prior to each test, each suspension of the test vehicle be placed in a nominally neutral

roll condition (i.e. with respect to hysteresis resulting from Coulomb friction). Means to do this may include, but

are not limited to, the following.
⎯ Reinstall the vehicle on the table prior to each test.

⎯ For suspensions with steel springs, unload the suspension by jacking up the sprung mass and then lower

the sprung mass while maintaining nominally zero roll.

⎯ For suspensions with air springs, substantially displace the suspension vertically by inflating/deflating the

air springs equally on left and right sides.

NOTE Initial conditions of hysteresis in the suspensions do not typically have a significant effect on the steady-state

rollover threshold of the vehicle. Initial conditions do, however, influence the behaviour of the vehicle in earlier stages of

the tilting process.
8.1.6.2 Suspension ride heights

Immediately prior to each test run, all self-regulating suspensions shall be adjusted such that they are at the

proper ride height or, in the case of the suspensions for certain auxiliary axles, at the prescribed inflation

pressure. Initial ride height of each suspension shall be reported.
8.2 Test tilts

Tests shall be conducted tilting the vehicle to the left and to the right. Alternatively, if the vehicle is known to

be less stable in one direction, tests may be conducted only in that direction.

A minimum of three tests should be performed in each direction in which testing is conducted.

During the tilting process, the variation of tilt angle between the positions of support of the individual axles

shall be within ± 0,1°.

Tests shall be initiated at a tilt angle of 0 ± 0,5°. Tilt rate should not exceed an absolute value of 0,05°/s in the

vicinity of events of interest (e.g. wheel lift). This is particularly important when the vehicle is going through

lashes in suspensions or couplings. At such times, especially if the tilt rate is higher than 0,05°/s, it is

recommended to pause the tilting and let the vehicle stabilize before the tilting is continued. It is permissible

(and often advantageous) to pause the tilting process at any time during a test. However, tilt angle should not

be reduced during a test. Tilting should be stopped as quickly as possible following the critical wheel lift.

When the test vehicle is equipped with self-regulating suspensions, the tilt-table shall be returned to the level

condition as soon as practicable following the test, and the final state of the suspensions shall be determined

and reported. If final conditions vary significantly from initial conditions as a result of malfunctions, such as air-

system leaks, the malfunctions shall be corrected and the test shall be repeated.

© ISO 2011 – All rights reserved 7
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ISO 16333:2011(E)

Prior to actual tests, it is recommended that one or more preliminary tilts be conducted. The purposes of a

preliminary tilt may include but are not limited to the following:

⎯ proper adjustment of the safety restraints for arresting roll motion of the vehicle;

⎯ establishing the sequence and approximate tilt angles at which wheel lift and other significant events take

place;
⎯ identifying the critical wheel lift;
⎯ initial installation of wheel lift indicators (e.g. switches).

Specific actions in a preliminary tilt depend on the specific design of the tilt-table facility. Typically, a

preliminary tilt would be initiated with safety restraints adjusted in a very conservative manner, i.e. in a manner

that would not allow all the free roll motion of the vehicle as required during an actual test. The tilt would be

proceeded with cautiously, with several pauses, typically at wheel lift points, for readjustment of safety

restraints.
9 Data analysis
9.1 General

General data shall be presented in the test report in accordance with ISO 15037-2:2002, Annexes A and B,

and in accordance with Annex A of this International Standard. For every change in equipment of the vehicle

(e.g. load), the general data for the vehicle shall be documented again.
9.2 Tilt-table ratio

The tilt-table ratio (TTR) shall be determined for each test run. When tilt angles are measured individually for

each axle, φ shall be determined from the average of the individual angles at critical wheel lift.

For each direction of tilt, the mean value of the estimates and the 90 % confidence interval of the mean value

shall be determined and reported. The lesser of the means shall be taken as the estimate of steady-state

rollover threshold for the vehicle.

NOTE Good experimental practice ought to result in run-to-run repeatability of TTR of better than 0,005.

90 % confidence intervals of 0,001 for the mean estimate of TTR from three or four tests are not unusual. Repeatability of

significant events prior to instability is often somewhat less.
9.3 Optional data presentations
9.3.1 Wheel-lift events
Estimates of the lateral accelerat
...

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